In a statement, the deputy information commissioner Graham Smith said emails between scientists at the university's Climatic Research Unit (CRU) that were hacked and placed on the internet in Novemberrevealed that FOI requests were "not dealt with as they should have been under the legislation".

Some of the hacked emails reveal scientists encouraging their colleagues to delete emails, apparently to prevent them from being revealed to people making FOI requests. Such a breach of the act could carry an unlimited fine, but Smith said no action could be taken against the university because the specific request they had looked at happened in May 2008, well outside the six-month limit for such prosecutions under the act.

The hacked emails have created an international argument that has fuelled climate scepticism and led to questions about the operation of the UN's climate science body, the Intergovernmental Panel on Climate Change (IPCC).

The pronouncement by the Information Commissioner's Office is likely to carry significant weight with the inquiry. The illegal hack is separately also being investigated by Norfolk police.

"I think that is an extremely serious charge," said Phil Willis, the Liberal Democrat MP who chairs the parliamentary science and technology select committee, which is conducting its own inquiry. He said that Smith's statement would be investigated by both the select committee and Russell's inquiry. "I don't think you can have the inquiry unless you have all the issues relating to it out in the open."

Willis said it would be wrong if there could be no legal sanction had the FOI act been breached. "Given the seriousness of this issue, the fact that it has caused global consternation, and has given ammunition to the climate sceptics – to have such a serious breach and for there to be no recourse in law requires urgent attention by the government."

He urged the university to be open with the data that was being requested. "If there has been a breach in this situation then the most honourable thing for the university to do would be to honour the request in its totality with all speed," said Willis.

Smith's statement refers to an FOI request from a retired engineer and climate sceptic in Northampton called David Holland. The CRU had been bombarded with similar requests for data, and the hacked emails between scientists suggest they were extremely frustrated with having to deal with them.

In response to the request, Dr Caspar Ammann, a scientist at the National Centre for Atmospheric Research in Boulder, Colorado, wrote back to three scientists, including the CRU's director, Dr Phil Jones: "Oh MAN! Will this crap ever end??"

In his statement, Smith said that Holland's request was not dealt with correctly by the university. "The emails which are now public reveal that Mr Holland's requests under the Freedom of Information Act were not dealt with as they should have been under the legislation. Section 77 of the Freedom of Information Act makes it an offence for public authorities to act so as to prevent intentionally the disclosure of requested information."

But he added that it was now too late to take action because the legislation requires that sanctions are imposed within six months of the offence. "The ICO is gathering evidence from this and other time-barred cases to support the case for a change in the law. It is important to note that the ICO enforces the law as it stands – we do not make it."

He said he would be advising UEA on its legal obligations. "We will also be studying the investigation reports [by Sir Muir Russell and Norfolk police], and we will then consider what regulatory action, if any, should then be taken under the Data Protection Act."

Bob Ward, policy director at the Grantham research institute on climate Change and the environment at the London School of Economics, said: "I think that anybody reading the emails that have been posted online will have concluded that some of those showed an intention to avoid complying with the FOI. I always thought that those emails were the most damning.

"I think this is quite damaging. It remains to be seen why these requests were not handled properly. I think regardless of any action by the information commissioner, the university should clearly take appropriate action in response to this."

A spokesperson for the University of East Anglia said that it was not aware of Smith's statement. "The way Freedom of Information requests have been handled is one of the main areas being explored by Sir Muir Russell's independent review. We have already made clear that the findings of the review will be made public and that we will act as appropriate on its recommendations," she said.